The present invention relates to a lubricating device for a scroll compressor which is used, for instance, in an air conditioning unit or a refrigerating unit for low temperature service.
The principles of a conventional scroll fluid machine will be described briefly.
FIGS. 1A to 1D show the fundamental components and illustrate the compression principles of a conventional scroll compressor. In these figures, reference numeral 1 designates a stationary scroll; 2, an orbiting scroll; 3, an intake chamber; 4, a discharge port; and 5, compression chambers. Further, reference character O designates the center of the stationary scroll 1.
The stationary scroll 1 and the orbiting scroll 2 have spiral arms or wraps 1a and 2a, respectively, which are similar in configuration to each other but which are wound in opposite directions. The configuration of the wraps 1a and 2a is that of an involute curve or arc, as is well known in the art.
The operation of the scroll compressor will be described. The stationary scroll 1 is held at rest, and the orbiting scroll 2 is combined with the stationary scroll 1 with a phase difference of 180.degree. therebetween. The orbiting scroll 2 revolves around the center O of the stationary scroll 1 without itself rotating. That is, the orbiting scroll 2 is turned in a manner as illustrated in sequence in FIGS. 1A through 1D, which show the orbiting scroll at positions of 0.degree., 90.degree., 180.degree. and 270.degree., respectively. When the orbiting scroll 2 is positioned as shown in FIG. 1A, the gas in the intake chamber 3 is enclosed and compression chambers 5 are formed by the wraps 1a and 2a. As the orbiting scroll 2 turns, the volume of each of the compression chambers 5 is progressively reduced to compress the gas therein. As a result, the gas in each compression chamber is discharged through the discharge port 4 provided at the center of the stationary scroll 1.
The basic principles of the scroll compressor are disclosed in U.S. Pat. No. 801,182 to Creux. Although the principles of the scroll compressor have long been understood, it was not put to practical use for many years for following reasons: As shown in FIGS. 1A through 1D and described above, the wraps of the stationary and orbiting scrolls are combined together and the orbiting scroll is moved in such a manner that it revolves around the center of the stationary scroll without itself rotating. So that this can be done smoothly and without significant leakage, the wraps must be machined with high precision. Because the compression chambers are intricate both in configuration and in construction, it is difficult to maintain the compression chambers closed. Furthermore, as the wraps wear, it becomes difficult to maintain the compression chambers tightly sealed.
In the 1970s, an improved technique of sealing the ends of the wraps was developed. Further improvements have also been made in the machining techniques used to manufacture the wraps. In 1982, mass-produced open scroll compressors were put on the market in Japan. The construction of these open scroll compressors is substantially the same as the scroll compressor disclosed, for instance, in U.S. Pat. No. 4,314,796. In the open scroll compressor, sliding parts such as bearings are lubricated mainly with a splash lubrication arrangement similar the type employed in a conventional reciprocation-type compressor.
Mass-produced closed scroll compressors were put on the market in Japan in 1983. In the lubricating arrangement of the closed scroll compressor, the lower end portion of a hollow vertical crankshaft used to drive the orbiting scroll is immersed in an oil pool, and compressed gas is applied to the oil pool so that lubricant from the pool is forced through the central hole of the hollow vertical crankshaft and then applied to sliding parts such as bearings.
The principles of the above-described method of utilizing the pressure of compressed gas to apply lubricant through the central hole in the crankshaft to sliding parts is disclosed in Japanese Laid-Open patent application No. 46081/1980 to Sugihara et al., especially in FIG. 20 thereof.
In another lubricating arrangement for a closed scroll compressor, as shown in FIG. 21 of the above-mentioned Japanese Laid-Open patent application No. 46081/1980, a lubricating path is formed in the crankshaft extending along an axis offset from the central (longitudinal) axis of the crankshaft. In this arrangement, the lubricant from the oil pool is sucked up by a centrifugal force caused by the rotation of the crankshaft. That is, the lubricating device is a self-actuated suction type. Further, it has been found by the present applicants that, in the case where a self-actuated suction type lubricating device is employed and a crankshaft driving motor is interposed between the orbiting scroll and the oil pool, the bearing supporting the upper end of the crankshaft must be positioned considerably high above the surface of the lubricant in the oil pool and must be restricted in size. This results in considerable resistance to the flow of lubricant, as a result of which it is difficult to sufficiently lubricate this bearing, and therefore the bearing is liable to wear quickly, sometimes even seize. These difficulties are exasperated by the fact also that the self-actuated suction-type lubricating device has only a small pumping capacity. These difficulties can be alleviated to some extent by increasing the diameter of the crankshaft so that the distance between the oil path formed in the crankshaft and the central axis of the crankshaft can be increased. However, such an increase of the diameter, and hence also of the weight, of the crankshaft causes other problems, including an increase in the required output power of the motor. Accordingly, the overall diameter of the compressor is excessively great.